A superconducting coil formed by helically winding a superconducting wire is used in a very low temperature. Therefore, in a superconducting apparatus including a superconducting coil, such as a motor, the superconducting coil is used while being held in a container. The superconducting coil is used in a cooled state by supplying a coolant such as liquid nitrogen into the container.
Japanese Unexamined Patent Application Publication No. 2007-35835 (Patent Document 1), for example, describes an existing method of making an inner container of a cryostat for storing a coolant having a very low temperature and holding a superconducting coil therein.